The present application is based on Japanese Patent Application No. 2001-308620, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a boot for covering a constant velocity joint that is served as a joint for a drive shaft of the front-wheel-drive vehicle for protecting the joint portion of the constant velocity joint from invasion of water or dust.
2. Related Art
Hitherto, the joint portion of the constant velocity joint is covered by an accordion-folded boot in which grease is encapsulated and is protected from invasion of water or dust, so that smooth revolution at broad angle is ensured. The constant velocity joint boot includes a larger cylindrical portion of large diameter to be held by a joint outer race, a smaller cylindrical portion being smaller than the larger cylindrical portion in diameter to be held by a shaft, and a bellows portion of substantially conical shape for integrally connecting the larger cylindrical portion and the smaller cylindrical portion. When in use, the bellows portion deforms in accordance with the angle (joint angle) formed between the joint outer race and the shaft, and thus the joint portion is reliably sealed by the boot even when the angle increases.
In past days, the constant velocity joint boot used to be formed of rubber in many cases. However, since rubber has a problem in durability, thermoplastic elastomer being superior in weather resistance and in fatigue resistance is used in recent years. On the other hand, the constant velocity joint boot is required to be provided with a sealing performance to prevent water or dust reliably from invading into the joint. However, there was such problem that thermoplastic elastomer, when being employed as material, cannot ensure enough sealing performance as rubber because of its low resiliency. Though blow molding is convenient as a method for forming the constant velocity joint boot, it is difficult to form the shape of the inner peripheral surface of the larger cylindrical portion so as to have a high sealing performance by blow molding. Therefore, it is difficult to ensure a sealing performance with respect to the mating member from these points of view.
Accordingly, in JP-U-02-87131, a constant velocity joint boot in which the boot body is formed of polyester thermoplastic elastomer, and a ring-shaped bushing formed of soft rubber is inserted into the larger cylindrical portion thereof is disclosed. According to the constant velocity joint boot of this type, the bushing can be manufactured with a high degree of accuracy by injection molding or the like. Therefore, the shape accuracy of the boot body does not have to be so high, and thus the boot body may be manufactured by blow molding. A tightening force from the clamp is transmitted to the bushing via the larger cylindrical portion, and resilient deformation and hence tight adherence of the bushing with the mating member establish the sealing performance. In other words, durability is established by the boot body and the sealing performance with respect to the mating member is established by the bushing. Furthermore, the boot body, being larger in shape than the bushing, may be manufactured by blow molding, which results in reduction of the number of process and hence of the costs.
However, when manufacturing the boot body by blow molding, there remains such problem that the accuracy of the internal surface and the accuracy of the thickness are poor. Therefore, in the case of a constant velocity joint boot of a structure having a soft bushing inserted into the larger cylindrical portion of the boot body, when the thickness of the larger cylindrical portion varies, uniformity of the pressure exerted on sealing surface with respect to the bushing is impaired. As a consequent, there is a case in which the sealing performance between the boot body and the bushing is lowered, and thus problems such as leakage of grease arise.
With such circumstances in view, it is an object of the invention to provide a constant velocity joint boot of a construction having a soft bushing inserted into the larger cylindrical portion in which a high sealing performance with respect to the bushing is ensured even when the dimensional accuracy of the larger cylindrical portion is low.
A constant velocity joint boot according to the invention in which the aforementioned problem is solved is a constant velocity joint boot comprising:
a boot body made of a first material including
a smaller cylindrical portion attachable to a shaft,
a larger cylindrical portion disposed coaxially with and at a distance from the smaller cylindrical portion and being larger than the smaller cylindrical portion in diameter, and
a conical bellows portion connecting the smaller cylindrical portion and the larger cylindrical portion; and
a ring-shaped bushing formed of a second material that is softer than the first material and having a sealing projection to be engaged with a mating member on an inner peripheral surface thereof, the boot body and the bushing being tightened on the mating member by reducing diameters thereof from the outer peripheral surface of the larger cylindrical portion;
at least one ring-shaped ridge formed on an outer peripheral surface of the bushing and extending in a circumferential direction of the boot body, the ring-shaped ridge being configured so as to fall down toward a side where the bellows portion is provided in a longitudinal direction of the boot body when the ring-shaped ridge is pressed by the larger cylindrical portion.
The ring-shaped ridge is preferably formed on the outer periphery at the position corresponding to the sealing projection. The ring-shaped ridge and the sealing projection may be formed on a common plane which is normal to an axial direction of the bushing. The ring-shaped ridge may be formed in parallel with the sealing projection.
The ring-shaped ridge may be triangular in cross section, and an angle formed between a raising surface of the ring-shaped ridge which is oriented to the bellows portion and the outer peripheral surface of the bushing is not more than 90 degrees.
Further, a groove which is in parallel with the ring-shaped ridge may be formed on the outer peripheral surface of the bushing so that the groove is engaged with the sealing projection of the larger cylindrical portion.
In the constant velocity joint boot of the invention, preferably a pair of the ring-shaped ridges are provided on the outer peripheral surface of the bushing and the groove is located between these two ring-shaped ridges in parallel therewith in the circumferential direction of the boot body.
A constant velocity joint boot of the invention is formed with a ring-shaped ridge on the outer peripheral surface of the bushing so as to extend in the circumferential direction, and the ring-shaped ridge is capable of falling toward the bellows portion when the larger cylindrical portion is brought into press contact therewith. In other words, in a state in which it is tightened by the mating member, the ring-shaped ridge being fallen toward the bellows portion is interposed between the larger cylindrical portion and the bushing, and the ring-shaped ridge is brought into press contact with the larger cylindrical portion by a resilient reaction force of its own. When a pressure is exerted from grease contained in the bellows portion, since the pressure acts in the direction to allow the ring-shaped ridge to restore its original posture, the ring-shaped ridge is further brought into press contact with the inner peripheral surface of the larger cylindrical portion. In other words, since the ring-shaped ridge serves as a dam and is brought into press contact with the larger cylindrical portion at a high bearing pressure, problem such as leakage of grease may reliably be prevented. With these actions, even when there are variations in thickness or shape of the larger cylindrical portion, a high sealing performance is established between the larger cylindrical portion and the bushing.
The ring-shaped ridge is preferably formed on the outer periphery thereof at the position corresponding to the sealing projection. Accordingly, a tightening stress is reliably transmitted from the ring-shaped ridge to the sealing projection, and thus a high bearing pressure may be established. Therefore, the sealing performance between the bushing and the mating member is further improved.
The number of the ring-shaped ridge may be one, but it is preferable to form a pair (two) of ring-shaped ridges substantially symmetrically along the length of the bushing. Accordingly, since a tightening stress is uniformly transmitted from the larger cylindrical portion to the bushing, variations in dimensional accuracy of the larger cylindrical portion may further be absorbed, thereby securing higher sealing performance. In this case, at least the inner (on the side of the bellows portion) ring-shaped ridge is configured in such a manner that it can be fallen toward the bellows portion when the larger cylindrical portion is brought into press contact therewith. The configuration of the outer ring-shaped ridge is not specifically limited, but when the same configuration as the inner ring-shaped ridge is employed, the outer ring-shaped ridge falls toward the bellows portion, thereby preventing leakage of grease over again. When the configuration that is capable of falling toward the outside is employed, the sealing performance with respect to water or dust invading from the outside may be improved.
Less number of ring-shaped ridges is preferable. When a large number of ring-shaped ridges are provided, a tightening force is dispersed correspondingly, and thus the bearing pressure between the respective ring-shaped ridges and the larger cylindrical portion is reduced. Therefore, the sealing performance is lowered. As a consequent, most preferably, a pair of (two) ridges are formed substantially symmetrically along the length of the bushing.
The configuration of the ring-shaped ridge may be, for example, triangular in cross section, and the angle formed between the surface extending toward the bellows portion and the outer peripheral surface of the bushing is not more than 90 degrees. In this arrangement, when being compressed by the larger cylindrical portion by being tightened, the ring-shaped ridge falls to form an angle not more than 90 degrees. Therefore, it falls reliably toward the bellows portion. The angle is preferably between 45 degrees and 90 degrees inclusive, and more preferably between 60 degrees and 90 degrees inclusive. It is also possible to form a ring-shaped recessed groove extending in the circumferential direction of the bushing on the surface of the ring-shaped ridge extending toward the bellows portion. In this case, when being compressed by the larger cylindrical portion by being tightened, since the ring-shaped ridge is bent along the recessed groove and hence is easily deformed, it falls reliably toward the bellows portion. Alternatively, the side of the ring-shaped ridge extending toward the bellows portion may be formed of material softer than that of the other side.
The boot body is preferably formed of thermoplastic elastomer for example of polyester group or of polyolefin group. This contributes to increase durability of the boot. Furthermore, though the method of molding is not specifically limited, it is preferable to form the boot by blow molding in terms of the cost. In the case of blow-molded boot body, it is difficult to control the configuration of the inner peripheral surface of the larger cylindrical portion, and the dimensional accuracy of the thickness is also low. However, according to the invention, even with such a boot body, a high sealing performance may be established with respect to the bushing.
Material of the bushing must simply be softer than the boot body, and polyolefin thermoplastic elastomer (TPO) or rubber, which is less expensive, may be employed. The molding method is not specifically limited, and thus compression molding, injection molding, or the like maybe employed. The ring-shaped ridge and the sealing projection, being formed integrally with the bushing, are soft and thus exhibit a high sealing performance when being tightened.
For reducing the diameter physically from the outer peripheral surface of the larger cylindrical portion, a clamp or the like may be employed as in the related art.